Preparation of high-consistency tomato juice



United States Patent Ofifice A 3,366,496 Patented Jan. 30, 19683,366,490 PREE'ARATION F HIGH-CGNSESTENCY TGMATO JUICE Joseph R. Wagner,Moraga, Jackson C. Miers, Pleasant Hill, and Horace K. Burr, El Cerrito,Califi, assignors to the United States of America as represented by theSecretary of Agriculture Continuation-impart of appiication Ser. No.439,488,

Mar. 12, 1965. This application Nov. 4, 1966, Ser.

13 Claims. (Cl. 99-1fl5) A nonexclusive, irrevocable, royalty-freelicense in the in the invention herein described, throughout the worldfor all purposes of the United States Government, with the power togrant sublicenses for such purposes, is hereby granted to the Governmentof the United States of Arnerica.

This application is a continuation-in-part of our copending priorapplication Ser. No. 439,488, filed Mar. 12, 1965, now abandoned.

This invention relates to and has among its objects the provision ofnovel processes for preparing tomato juice of high consistency. Furtherobjects of the invention will be evident from the following descriptionwherein parts and percentages are by Weight unless otherwise specified.

The annexed drawing is a flow sheet illustrating application of theprocess of the invention.

It is recognized in the industry that consistency is an importantattribute of tomato juice. In particular, higher consistency representsbetter quality. It is to be especially noted that consistency has nofixed relationship with solids contents so that whereas two lots oftomato juice prepared by different procedures and/or different rawmaterials may have identical solids contents, their consistencies may beradically different. The matter of consistency is not only importantwith regard to tomato juice per se but also with regard to productsprepared therefrom such as concentrated juice, pastes, sauces, ketchups,etc. In all these products a higher consistency signifies better qualityand to attain such quality it is necessary that the juice employed asthe starting material be of high consistency.

Those familiar with the art are aware that consistency of tomato juicemay be controlled to some extent by the method of manufacturing thejuice, particularly by choice of the cold-break method or the hot-breakmethod. In the cold-break method, raw tomatoes are macerated at ambienttemperatures and the resulting pulp is pressed through perforated sheetmetal or wire mesh screens to separate the juice from the seeds, skins,cores, etc. This process yields a juice of relatively low consistencydue, it is believed, to degradation of pectin-containing colloids byenzymes such as pectinesterase and polygalacturonase which naturallyoccur in the fruit. In the hot-break method, the same mechanical stepsare used but in addition heat is applied, i.e., the tomatoes-duringmaceration or immediately after they are broken up-are quickly heated toa temperature of 185 F. or higher so as to inactivate the enzymesresponsible for the loss of consistency. The juice obtained in thistechnique has a higher consistency than that produced by the cold-breaksystem and thus the hot-break procedure is generally preferred inindustry.

Application or" the techniques of the present invention providesadvantages over those attainable with the known processes. As anexample, the process of the invention may be applied in conjunction withthe known hot-break method whereby to yield a juice of substantiallyhigher consistency than obtained with the usual hot-break system.Moreover, although the procedure of the invention is preferably appliedin conjunction with hot-break sys tems, it can also be advantageouslyapplied in cold-break systems. In such case the juice product will havea higher consistency than obtained with the standard cold-break systemthough it is not claimed that the consistency will be as high as wherethe invention is applied in conjunction with heat. One advantage ofutilizing the invention in conjunction with the cold-break method isthat it can be practiced in a plant having equipment designed foroperation at ambient temperatures and the modification will permitproduction of juice of consistently high consistency.

In accordance with the invention, the basic step to achieve a juice ofincreased consistency involves macerating raw tomatoes in the presenceof added acid. The verb macera'te is employed herein-in common with itsusage in the artto denote application of mechanical action to break upor subdivide the tomatoes into a pulpy mass.

For use as the added acid, we prefer hydrochloric acid because it iseffective, inexpensive, and particularly because eventual neutralizationof the product (with sodium hydroxide) yields sodium chloride-a commonadditive in tomato products. The hydrochloric acid may be added as suchor in the form of hydrogen chloride gas. Moreover, acids other thanhydrochloric can be employed as the primary consideration is theestablishment of a low pH. Thus, for example, one may employ suchstronglyionized acids as sulphuric, orthophosphoric, metaphosphoric, andpyrophosphoric. Weaker acids such as tartaric or citric may also beused. However, though effective, these weaker acids are not preferredbecause large proportions are required to attain the necessary reductionin pH. Acetic acid is too weakly-ionized to be of any practicalusefulness. In view of the above considerations, generically one mayemploy any acid which is more strongly ionized than acetic (i.e., has anionization constant greater than l.86 lO and which is nontoxis. It is,of course, within the scope of the invention to use mixtures of two ormore acids, for example, a mixture of hydrochloric and any of thephosphoric acids.

In general, it has been observed that addition of enough acid toestablish a pH in the macerate of less than 3.5 will provide an increasein consistency over that attained in the absence of added acid.Moreover, as the pH is reduced below the aforesaid level, greaterincreases in consistency are achieved. It has also been observed that asthe pH is reduced below about 2, little if any further increase inconsistency is attained. Thus, whereas the pH may be decreased to verylow levels, there is no practical purpose gained by going below a pHof 1. Usually, we prefer to operate at a pH range of about 2.5 to about3.0- particularly in a system where maceration is conducted hot 'herebya large increase in consistency is achieved without requiring excessiveamounts of added acid. As noted hereinabove, the primary considerationof the added acid is to establish a reduced pH. However, there is somevariation in effect between different acids applied at the same pH andthis is particularly noticeable with metaphosphoric acid which providesa virtually maximum increase in consistency at a pH of 2.97.

Although reduction in pH, as described above, is the critical factor toproduce juices of increased consistency, there will be variation in thelevel of consistency attained at any given pH, depending on such factorsas the nature of the tomatoes being treated, the temperature at whichthe treatment is carried out, and-if a heated system is used-the rate atwhich the material is heated. For example, at the same pH a hot-breakprocedure will usually yield a product of higher consistency than will acoldbreak procedure. Moreover, within the realm of hot-break procedures,a product of especially high consistency will be attained Where thetreatment is conducted under conditions to attain a rapid comminutionand heating of the acidified tomato material. In view of the aboveexplanation of the influence of heat, it is evident that if one isaiming at producing a juice that exhibits a particular degree ofconsistency increase, one would correlate the type of process with pHlevel used. For example, if the cold-break system were chosen one woulduse a lower pH than would be the case were the processing done by thehot-break system.

As noted above, the benefits of the invention are achieved by maceratingthe raw tomatoes in the presence of added acid. The primary action ofthis maceration step is to break up the fruit and mix it with the acidso that there is intimate contact between the acid and the tomatomaterial, including both liquid and cellular particles. In order toachieve the desired result of a high-consistency juice, it is necessarythat the acid be present at the time the tomato structure is broken upand for this reason it is preferred to add the acid to the tomatoeswhile they are still whole or at most after they have been cut intopieces. When this is done, the acid contacts the particles of tomatomaterial as these particles are formed by the comminution of the fruit.As a result, the enzymes and enzyme substrates released by thedisorganization of natural structure have little or no opportunity toreact. On the other hand, were the tomatoes to be broken up as such andthen mixed with acid, substantial loss of consistency would occurbecause of the interaction of released enzymes and enzyme substratesbefore the acid could do its work. The effect of the acid is rapidlyrealized so that the maceration need only be conducted for a shortperiod of time, e.g., about from seconds to 5 minutes, depending mainlyon the efficacy of the equipment used to effectuate the maceration. Forproduction of juice of maximum consistency the macerate is heated to atemperature of at least 185 F., preferably about 200 F. The heating maybe applied after completion of maceration but, preferably, heat isconcomitantly applied as the tomatoes and added acid are subjected tomaceration. At any rate, after the tomatoes have been broken down to apulp and intimately mixed with the acid, with or without heating, thepulp without any delay is passed through conventional .equipment toseparate the juice from the skins, seeds,

cores, etc. It is a noteworthy advantage of the invention that, ingeneral, the amount of this waste (skins, etc.) is less, as much as40-50% less, than that with conventional juice production. Anothernoteworthy advantage of the invention is that the desired enzymeinactivation is attained by the addition of a single chemicala simpleacid-and no other substances are required.

It is obvious that addition of the acid will produce a juice ofexcessively sour taste. Accordingly, the product is neutralized to itsnormal pH (usually in the range 3.8- 4.2) by incorporation of sodiumhydroxide. Other alkaline materials such as sodium carbonate orbicarbonate may be used but are not preferred because of their foamingeffect (caused by release of C0 The neutralization can be applied to thejuice or, preferably, to the macerate prior to passing it to the juiceextractor. In the event that a coldbreak system is used, the juice (ormacerate) should be heated to an enzyme-inactivating temperature (185 to212) before application of the neutralization step. Such heating willprevent loss of consistency when the effect of the added acid iscanceled by the neutralization.

A particular advantage of the invention is that it can be applied toconventional juice production lines with but minor changes. Thusstandard juice production involves a maceration of the fruit at an earlystage in the line and the acid can be introduced into the maceratingdevice with conventional metering equipment. For the neutralization oneneed only provide a mixer and a device for introducing alkaline materialat the appropriate rate whereby the macerate (or the juice) is broughtto its original pH. It may be noted that such changes in the standardproduction pattern do not contribute any interference with flow of thetomato material through the system. Thus addition of the acid does notinterfere with or prolong the maceration step and the neutralizationstep likewise does not cause any delay in transferring the pulp (fromthe macerator) to the juice extracting step. A typical adaptation of astandard continuous juice production line to operate in accordance withthe process of the invention is illustrated in the flow sheet in thedrawing annexed hereto.

Referring to the flow sheet, .raw tomatoes are continuously fed at apredetermined rate into macerator 1 together with a flow of acid meteredto provide the proper pH. In macerator 1 the tomatoes are rapidlycomminuted and intimately mixed with the acid and concomitantly heatedto about 200 F. The resulting macerate flows to mixer 2 wherein it isblended with a stream of sodium hydroxide solution metered torestore'the macerate to its natural pH level. The neutralized macerateis then directed to screw press 3 to separate the juice from the skins,seeds, etc. The juice issuing from the screw press may then be processedin known manner to produce canned. juice, concentrated or dehydratedproducts, etc.

Tomato juice prepared in accordance with the invention may be processedin conventional manner. For example, it may be canned as asingle-strength juice or it may be first concentrated to a paste orpuree and canned in such state. It may be used, in single strength orconcentrated form, in the preparation of soups, sauces, ketchups,preserves, aspic products, etc. Also it may be converted into soliddehydrated products by such known techniques as concentration followedby foam-mat or vacuum dehydration or by spray drying. It is an importantfeature of the invention that the color, flavor, and nutrient value ofthe juice are not impaired so that it is suitable for all the uses forwhich conventional tomato juice is adapted.

Since the process of the invention produces a highconsistency juice,this product can be blended with conventional juices (ones of lowerconsistency) to provide a composite juice of intermediate consistency asmay be required for a particular application. As an example of suchprocedure, a juice processing line may be operated for a first period oftime in conventional manner and operated for a second period of timewith application of the process of the invention, the two juices beingthen combined to yield the final product. By varying the relativeduration of the first and second periods, products of a wide range ofconsistency can be produced.

The invention is further demonstrated by the following illustrativeexamples. The explanatory notes in Paragraphs A through E, below,concern Examples I to IV.

(A) The macerating and blending operations referred to in the exampleswere carried out in a large Waring Blendor equipped with a l-gallon bowland a rotating blade assembly in the base of the bowl to out and blendthe material contained therein. Where the material was to beconcomitantly heated, a steam-heated coil was inserted in the bowl incontact with the material undergoing treatment.

(B) In all the examples, except Example II, the following procedure wasapplied: After maceration and blending, with or without application ofheat, the juice was extracted from the macerate by passing the latterthrough a tapered screw-type extractor provided with a perforated metalscreen (0.033 inch perforations).

(C) Consistency of the juice products was determined at C. (77 F.) bymeasuring the time required for 96 ml. of the liquid to pass through the3.3 mm. (I.D.) orifice of a 100-ml. pipette. With this test, a longerflow time refiects a higher consistency.

(D) For the products of higher solids content, a viscosity measurementwas made as follows: Using a Stormer viscosirneter fitted with alightweight opened spiral spindle, a determination was made of theweight required to revolve the spindle 100 times in seconds when thespindle was immersed in the sample at 25 C. (77 F.). In thisdetermination, a greater weight indicates a higher viscosity.

(E) In various of the examples, runs not representing the process of theinvention were included for purposes of comparison.

Example I.--Efiect of added HCl in preparing cold-break and hot-breakjuice Four kg. of ripe T-2 variety tomatoes were subdivided into fourcomparable l-kg. lots by quartering each fruit and distributing thequarters to the four lots. Each lot was then treated as follows:

Lot 1: Macerated and blended at room temperature for 1.5 minutes.

Lot 2: Eighteen ml. of concentrated hydrochloric acid were added to thetomatoes; maceration and blending at room temperature was then appliedfor 1.5 minutes.

Lot 3: Macerated and blended, initially at room temperature for 10seconds then with a steam coil in the system for an additional 102seconds to bring the macerate to 203 F.

Lot 4: Same treatment as with lot 3 except that 18 ml. of concentratedhydrochloric acid was added to the tomatoes before initiating theprocess.

Immediately following the above treatments, each lot was separatelypassed through the extractor. The juice from each lot was brought to 25C. (77 F.) and tested for consistency, density, and pH. The results aretabulated below:

It is evident from the above data that the acidification improved theconsistency of both the cold-break juice (lot 2 vs. lot 1) and thehot-break juice (lot 4 vs. lot 3) and that the combination ofacidification plus hot break (lot 4) provided the highest consistency.

The acidified hot-break juice (lot 4) was restored to the natural pHlevel (4.2) by addition of sodium hydroxide. Consistency of theneutralized juice was 117 sec., proving that the high consistency of theacidified hot-break product was a stable property.

In the case of the acidified cold-break juice (lot 2), directneutralization (to a pH of 4.2 with NaOH) caused a sharp drop inconsistency to 19 sec. This loss in consistency could, however, beprevented by heating the juice to an enzyme-inactivating temperature(1852l2 F.) prior to its neutralization.

Example H.Preparati0n of tomato paste A quantity of sound Ace tomatoeswas subjected to washing and trimming and then divided into two ZOO-lb.lots.

The first lot was put through a pulper (about 20 min. feeding time)equipped with a 0.033" screen. The juice was pumped from the pulper at11 lb. per min. through a Votator heat exchanger which heated it to210i4 F., then through a second Votator which cooled it to 138 F.Finally the juice was collected in a water-cooled pot in which it wascooled to F.

The second lot of tomatoes was subdivided into 3-kg. batches. Each batchwas macerated and blended with 54 ml. of cone. hydrochloric acid forabout 25 seconds. The macerates were combined and this compositemacerate was put through the pulper and heated and cooled exactly aswith lot 1. The pH of the juice was 1.03. A 12 N solution of sodiumhydroxide was slowly added to the juice until its pH was 4.42 (1350 ml.of NaOH solution was required).

Samples of the control juice (lot 1) and of the juice of'lot 2 (beforeand after neutralization) were collected during processing forconsistency measurements. The data are tabulated below:

Both lots of juice were then treated as follows: Evaporated in a vacuumpan at about 82 F. to a paste (2024 Brix). The paste was heated to -200F. poured hot into No. 2 /2 cans, sealed immediately and put intoboiling water for 3 minutes to sterilize the cans, cooled in runningwater to room temperature and put in storage at 34 F.

After one month storage at 34 F the cans of tomato paste were removedfrom storage and the pastes diluted to various densities and theviscosity of each diluted product measured. To correct for the saltpresent in the product of lot 2 (derived from the acidification andneutralization), each dilution was made to a designated level based onthe content of soluble tomato solids. The results are tabulated below:

Example III.--Eflect of difierent pHs A series of runs were made inwhich comparable samples of tomatoes (Ace variety) with varying amountsof hydrochloric acid to provide different pHs (as indicated below) weremacerated and blended, initially for a few seconds at room temperature,then with application of the steam-heated coil for 2.5 minutes to bringthe macerate to a temperature of 200 F. The macerates were then putthrough the extractor. The results are tabulated below:

Example I V.Use of various acids (other than HCl) The procedure ofExample III was repeated using various acids in place of thehydrochloric acid. The results are given below:

Example V These runs demonstrate the superior results achieved by usinga fast heating schedule. To achieve this, a dropin technique was used,that is, a heated (200 F.) pool of tomato juice was provided to serve asa direct-contact heating medium. Tomatoes were fed into this pool inportions, together with acid necessary to provide a desired pH level,while applying macerating action and heating to maintain the system at200 F. Because of the intimate contact with the hot juice, the enteringtomato material was very rapidly brought up to the desired temperature.More particulars of the procedure used are given below:

The runs were carried out employing a large Waring Blender equipped witha l-gallon bowl and a rotating blade assembly in the base of the bowl tocut and blend the material contained therein. A steam coil was alsoprovided for heating the material in the bowl.

At the beginning of each run, 500 grams of previouslyprepared tomatojuice Was adjusted to the same pH as was to be employed in the run,using the same acid designated for the run. This juice was placed in theblendor and heated to 200 F. and maintained at that level throughout therun while rotating the blade continuously.

A l-kg. lot of fresh tomatoes (cut into quarters) was divided into fourportions and these portions were fed into the hot juice at about secondintervals, together with an appropriate aliquot of the acid used in therun. At about 2 minutes from the start of the run, heating wasdiscontinued (by removing the steam coil from the bowl) but operation ofthe blade was continued to complete breakdown of any fragments of intacttissue. At 3 minutes from the start of the run the macerate was putthrough a pulper to separate the juice from the skins, seeds, etc. andthe juice was cooled. It was then tested for pH and consistency.

The juice used as the heated liquid for the runs was a conventionaljuice. It was prepared by macerating raw tomatoes at their natural pHwithout any additives, heating to 200 F. to destroy enzymes, andextraction of the juice from the maceratr- With a conventional pulper.

The results are tabulated below:

Consistency of juice 1 Run Acid added pH (Pipette 1) (Pipette 2) SecondsSeconds 1 Consistency (Pipette 1) was determined at 25 C. by measuringthe time required for 96 ml. of the juice to pass through the 3.3 mm.(I.D.) orifice of a 100-ml. pipette. Consistency (Pipette 2) wasdetermined in ghe same rgauner but employing a pipette with a largerorifice, namely,

In the above runs, the original juice used as the heat source carriedover into the product so that each product contained /3 part by weightof the original juice to part by weight of the acid-blended material. Itis evident that in continuous operation wherein the original juice wouldbe applied merely to start the operation and the fresh material wereadded over a considerable period 01 time with constant withdrawal ofproduct, the eifect of the original juice would be gradually eliminated.The end result would be, of course, that the system would attain asteady state wherein the products would exhibit higher consistenciesthan those obtained in the above laboratory runs.

Having thus described the invention, what is cliamed is:

1. A process for preparing tomato juice of increased consistency whichcomprises macerating tomatoes in the presence of added non-toxic acid inan amount to provide a pH less than 3.5 and extracting the juice fromthe resulting macerate.

2. The process of claim 1 wherein the acid is hydrochloric acid.

3. The process of claim 1 wherein the acid is hydrochloric acid in anamount to provide a pH of about 2.5 to 3.

4. The process of claim 1 wherein the acid is sulphuric acid.

5. The process of claim 1 wherein the acid is citric acid.

6. The process of claim 1 wherein the acid is orthophosphoric acid.

7. The process of claim 1 wherein the acid is metaphosphoric acid.

8. The process of claim 1 wherein heat is applied during the macerationto bring the macerate to a temperature of at least F.

9. The process of claim 1 wherein the macerate is neutralized to itsnatural pH by addition of non-toxic alkaline material, prior toextraction of the juice therefrom.

10. The process of claim 1 wherein the juice is neutralized to itsnatural pH by addition of non-toxic alkaline material.

11. The process of claim 1 wherein the juice is blended with a differentjuice of lesser consistency to provide a composite juice of desiredintermediate consistency.

12. A method for preparing high-consistency tomato juice which comprisesapplying hydrochloric acid, in an amount to provide a pH of about 2.5 to3, to raw tomatoes in a condition in which the tissue is largely in itsnatural orginized state, applying maceration and concomitant heating tothe mixture of tomatoes and added acid, continuing the maceration untilthere is produced a uniform intimate blend of comminuted tomato materialand acid, then without any substantial delay neutralizing the said blendto a pH of about 3.8-4.2 and extracting the juice therefrom.

9 19 13. A method for preparing high-consistency tomato References Citedjuice which comprises:

(A) providing a pool of macerated tomato material at UNITED sTATbSPATENTS a temperature f about 0 R 2,928,744 3/1960 Ponting 99-105 (B)continuously feeding raw tomatoes into said pool, 5 2,434,388 1/1958Brehm (C) concomitantly feedin hydrochloric acid into said pool in anamount to maintain the macerate at a pH 2291704 8/1942 Flsher 99 154 ofabout 2.5 to 3.0, OTHER REFERENCES (D) continuously maintaining thetemperature of the pool at about 200 F. and continuously applyin 10 iz gg; g g and Vegetable Jmces AVI macerating action thereto (E)continuously withdrawing a portion of the macerp Technology Effeqt fTomato can Structure on ated material from the p001, Consistency ofTomato Juice, vol. 11, pp. 1922, 1957. 2 fifgg f j f g g mammal PH of A.LOUIS MONACELL, Primary Examiner. (G) extracting the juice therefrom. M.VOET, Assistant Examiner.

1. A PROCESS FOR PREPARING TOMATO JUICE OF INCREASED CONSISTENCY WHICHCOMPRISES MACERATING TOMATOES IN THE PRESENCE OF ADDED NON-TOXIC ACID INAN AMOUNT TO PROVIDE A PH LESS THAN 3.5 AND EXTRACTING THE JUICE FROMTHE RESULTING MACERATE.